Tails in Sonic the Hedgehog
Original title: Sonic the Hedgehog
Platform: Sega Genesis / Mega Drive
Region: USA
Media: Cartridge
Controller: Gamepad
Genre: Platformer
Gametype: Hack
Release Year: 2007
Players: 1
Hacked by: drx
Version: 2.0
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Tails in Sonic 1 is a hack of Sonic the Hedgehog for the Sega Mega Drive/Genesis originally created by drx which featured Tails as a playable character instead of Sonic. Tails can fly, spindash and swim in the same way that he can in Sonic 3.

On June 8, 2007, Puto released an update to Tails in Sonic 1, which featured several improvements over the original hack: bugfixes, a corrected palette and Sonic 2-styled tired and swimming sprites. More bugfixes have been released since, and on 12/31/07, he released version 2.0, completely rewritten from scratch.

http://www.romhacking.net/hacks/389/